The invention relates to a method and apparatus for registering the presence of a moulding consisting of a biocompatible polymeric material, especially an ophthalmic lens, particularly a contact lens, in a package.
Mouldings consisting of a biocompatible polymeric material are usually placed in a package for storage and for transport. The packages in question are frequently so-called blister packages. A blister package consists of a plastic container, for example of polypropylene (PP), the top of which is sealed with film after the moulding has been placed in the plastic container.
In particular, contact lenses that are produced in large unit numbers, for example disposable contact lenses, are sealed into blister packages. Such contact lenses are preferably manufactured by the so-called mould or full-mould process. In this process, the lenses are manufactured into their final shape between two moulds, so that there is no need to subsequently finish the surfaces of the lenses, nor to finish the edges. Mould processes are described for example in PCT application no. WO/87/04390 or in European patent application EP-A-0 367 513.
To manufacture a contact lens, first of all a certain amount of the flowable starting material is placed in the female mould half. Afterwards, the mould is closed by placing the male mould half thereon. Normally, a surplus of starting material is used, so that, when the mould is closed, the excess amount is expelled into an overflow area adjacent to the outer mould cavity. The subsequent polymerisation or crosslinking of the starting material takes place by radiation with UV light, or by heat action, or by another non-thermal method.
The contact lenses produced in this manner are moulded parts having little mechanical stability and a water content of more than 60% by weight. After manufacture, the lens is metrologically checked, then packaged and subjected to heat sterilisation at 121xc2x0 C. in an autoclave.
In U.S. Pat. No. 5,508,317, a new contact lens material is described, which is an important improvement in the chemistry of polymerisable starting materials for the manufacture of contact lenses. The patent discloses a water-soluble composition of a prepolymer, which is filled into the mould cavity and then crosslinked photochemically. Since the prepolymer has several crosslinkable groups, crosslinking is of particularly high quality, so that a finished lens of optical quality can be produced within a few seconds, without the necessity for subsequent extraction or finishing steps. Owing to the improved chemistry of the starting material as illustrated in the patent, contact lenses can be produced at considerably lower cost, so that in this way it is possible to produce disposable lenses.
Optical components produced in series, e.g. contact lenses, have to be checked for faults such as scratches, shrinkage or edges that have broken away. The components recognised as faulty are then rejected. However, at the moment there is no provision for checking whether a package has actually been filled with a contact lens. Under certain circumstances, empty packages may appear, which are not noticed. The client then discovers the empty package and is of course annoyed. However, if empty packages are recognised by chance or by spot checks, then either the whole batch has to be rejected or all the contact lens packages have to undergo 100% manual checking. Both procedures involve substantial costs.
The invention is therefore based on the problem of providing a testing method with which it is possible to detect, at low cost, whether a moulding, especially a contact lens, is actually present in the package.
The invention solves this problem with the features indicated in claim 1. As far as further essential refinements are concerned, reference is made to the dependent claims.
By measuring the temperature of a package, it is possible to establish the presence of mouldings in a package. Packages containing a moulding, especially a contact lens, have a characteristic change in their temperature compared with a package without a contact lens. By evaluating the temperature difference, it is possible to determine whether or not there is a contact lens in a package. In particular, by using the detecting method according to the invention, one can determine whether there is a contact lens in the package directly after the filling procedure. Further details and advantages of the invention may be seen from the description that follows and the drawing. In the drawing,